1. Field of the Invention
The present invention relates to the field of agriculture and crop sciences. More specifically, the invention relates to soybean lines that have been developed to have beneficial traits, including, but not necessarily limited to, low phytic acid content, low stachyose content, and high sucrose content.
2. Description of Related Art
The field of crop science involves, at least to some extent, developing new and improved crop plants that have beneficial characteristics. Those characteristics can be any of interest to those in the agriculture industry, but typically relate to disease or pest resistance, extreme water condition (e.g., drought, flood) tolerance, and improved nutritional value for animals and humans. Great effort and funding is expended in developing these new crops. Traditional development techniques include crossing of strains of a crop, and screening progeny for the presence or absence of a trait of interest. Newer methods include genetic engineering of plants by intentional insertion or deletion of genes known to be involved in particular biochemical pathways of interest.
Soybeans have traditionally been a staple of the diets of many cultures throughout the world. Increasingly, soybeans have become an important part of the diets of residents of the U.S. as well. Furthermore, soybeans are a major source of material for animal feed, particularly in the agricultural raising of animals for human consumption. Accordingly, an increasing number of studies have been instigated in the last twenty years to understand the biochemistry and genetics of soybeans and to develop improved strains of soybeans for human, and to some extent animal, consumption. Other studies have focused on improving the nutritional value of other plants that serve as a food source for animals and humans.
Soybeans contain several beneficial traits that make them advantageous as a food source for animals and humans. For example, soybeans are relatively high in protein content (about 40% by dry weight), relatively high in oil (about 21% by dry weight), and relatively high in soluble carbohydrate (e.g., sugar) content (about 11% by dry weight). Soybeans also contain useful amounts of phosphorus; however, much of the phosphorus exists in a form that is not directly available to animals and humans. Although soybeans are an excellent source of food for animals and humans, it has been recognized by the inventors that the nutritional value of soybeans can be increased by improvement of certain traits. Among those traits are available phosphorus content and available sugar content.
Phytic acid, or myo-inositol (1,2,3,4,5,6) hexakisphosphate, (also referred to as phytate when in its salt form) is typically the main form of phosphorus in plant seeds, including soybean seeds. It serves as a storage form for phosphate, and can be present in seeds at amounts exceeding 65% of total phosphorus. However, phytic acid is not highly digestible by animals and humans, and can actually decrease the nutritional value of the seeds by chelating nutritionally important minerals, such as calcium, zinc, magnesium, and iron, rendering those minerals unavailable for use by animals and plants consuming the seeds. To overcome this negative trait of seeds and provide a usable source of phosphorus for animals and humans, soybean food products are typically supplemented with either inorganic phosphate or the enzyme phytase (which catalyzes the breakdown of phytate). The addition of the enzyme phytase is costly and cumbersome, increasing the cost of production of food products. Furthermore, addition of inorganic phosphate raises the total phosphorus content of the food products, resulting in excess phosphate being ingested and ultimately excreted by the animal or human. In agricultural settings, the excreted phosphate becomes a pollutant to the environment, harming agricultural land and waterways that accept run-off from the agricultural land.
Stachyose is a significant form of soluble carbohydrate in seeds as well. However, stachyose is not digestible by monogastric animals, including humans and many agriculturally important animals, because these animals lack the enzyme a-galactosidase. The inability of these animals and humans to digest this sugar results not only in a waste of energy available from the seeds, but also can result in digestive problems for the human or animal consuming the seeds or products produced from the seeds. Thus, the inventors have recognized that development of a line of plants, such as soybean plants, having low stachyose content would improve the economic value of the plants as a food source.
It has been known in the art for over thirty years that expression of certain agriculturally relevant traits of soybeans are linked. For example, sucrose content of soybeans is known to be positively correlated with raffinose content and negatively correlated with stachyose content. Further, and not surprisingly, stachyose content is known to be negatively correlated with raffinose content. Soybeans are considered to behave like diploid organisms for most traits. They have been characterized as having 20 different chromosomes, and are thus typically regarded as having 40 chromosomes in the diploid state. Twenty molecular linkage groups (designated as A1, A2, B1, B2, C1, C2, D1a, D1b, D2, E, F, G, H, I, J, K, L, M, N, and O) have been identified in soybeans, which probably correspond to the 20 haploid chromosomes A1, A2, B1, B2, C1, C2, D1a, D1b, D2, E, F, G, H, I, J, K, L, M, N, and O.
Linkage of traits in soybeans, as in any other organism, can be considered from two different perspectives: physical linkage of genes in the genome, and expression of disparately located genes by way of similar expression control elements. For the purposes of traditional development or engineering of new and improved strains, the physical linking of genes is a key consideration. Using traditional development strategies, various traits are segregated based on the frequency of crossing-over events during generation of germ cells. In general, the closer two genes are to each other on the genome, the less likely they are to be separated by a crossing-over event. Statistical analyses can be performed, and values assigned to gene (trait) pairs, to give crop scientists an idea of how close two genes are on a chromosome, and thus how likely they are to co-segregate (i.e., how closely they are linked).
Numerous studies have been performed, and improved soybean lines developed over the years. For example, U.S. Pat. Nos. 6,653,451, 6,147,193, and 5,710,365 to DuPont/Pioneer, and a publication by Hitz et al. (Hitz, W. D. et al., 2002, Plant Physiology 128:650-660) disclose various improved soybean strains. Further, Wilcox et al. (2000) disclose the identification of mutations resulting in low phytic acid content in soybeans. These mutations were mapped by Walker et al. (Walker, D. R. et al., 2006, Crop Sci. 45:390-397) to linkage groups (LG) N at a locus near marker Satt237, and LG L at a locus near Satt527. Each of these references is hereby incorporated into this disclosure in its entirety by reference.
Although much research has been performed, and numerous improved soybean lines have been developed, the inventors have recognized that there still exists a need in the art for new, improved soybean lines that have beneficial characteristics. In particular, the inventors have realized that new soybean lines are needed that provide nutritional characteristics that are different and/or improved as compared to soybean lines now known in the art.